The present invention relates generally to nonlinear optical systems, and particularly to a new class of organic complexes capable of second harmonic generation.
The high light intensities available in coherent laser radiation have led to the development of nonlinear optical systems. The optical properties of materials are different at high intensities, since the electronic oscillators are driven so hard that anharmonic properties become evident. One such effect is harmonic generation of light, for example, conversion of red laser light to ultraviolet radiation of exactly doubled frequency. This effect known as second harmonic generation was first observed when quartz crystals were illuminated by laser radiation. Since this discovery, a number of inorganic and organic materials capable of second harmonic generation (SHG) have been discovered. A useful review of the state of the art relating to nonlinear properties of organic materials is provided by Williams, ed., Nonlinear Optical Properties of Organic and Polymeric Materials, (American Chemical Society 1983).
The nonlinear optical properties of organic and polymeric materials are currently under intensive study. Major research efforts are now directed towards searching for new molecules possessing large nonlinear polarizabilities and controlling molecular orientation on a microscopic level to influence bulk nonlinear optical properties. Over the past few years, research has indicated that organic molecules having conjugated pi electron systems or low-lying charge transfer excited states often possess extremely large second order polarizabilities. However, the potential of such molecules often cannot be utilized because of unfavorable alignment in the crystalline phase. In the case of SHG, second order susceptibility vanishes for centrosymmetric crystals.
A number of approaches have been taken to circumvent this problem. Use of a chiral molecule ensures formation of a noncentrosymmetric crystal and mathematically guarantees a nonvanishing second order susceptibility, but not necessarily a large one.
It has now been found that guest-host inclusion complexation can be used to control bulk nonlinear optical properties. Specifically, second harmonic generation by optically nonlinear aniline and aminopyridine compounds can be greatly enhanced by inclusion complexation with selected cyclodextrin compounds.